Two 21" CRTs I have are native XGA, hence 5:4.
Who talks about CRT in this LCD topic?
CRT monitors were all 4:3 (except one weird Sony)
But I still have to see the first 4:3 LCD at 19 inch.
No, there were a (very) few 5:4 CRT PC monitors. There was a cheep 19" at an old work that my boss liked running at 800x600, but complained about the images being "stretched". (IIRC that '19 inches' was viewable size, so 20"-21" tube size.) I've seen stats of an arcade CRT whose physical dimensions seemed to be closer to 3:2 instead of 4:3 (1.5 vs 1.333), and 16:10 = 1.6) for IIRC a vertical shooter, but can't find the link.
There were 17" & 20" LCDs at 5:4, too, but now almost all 5:4 LCDs are 19". AFAIK, all 19" LCDs were 5:4 (or, now more often, widescreen).
Sure, widescreen is great for movies, spreadsheets and horizontal PC games (driving, FPS), but 4:3 or 3:4 are sometimes better. Coding, writing for printed paper, reading book-ish stuff, editing portrait photos, etc. And since a widescreen has less screen area vs a 5:4 or 4:3, widescreen is cheaper to manufacture (for example 19": 5:4 area = 176 sq in, 4:3 = 173.25 sq in, 16:10 = 162.25 sq in).
With the hype, the move to LCDs, the cheaper to make, HDTV, and economies of scale, widescreen is going to be the only option soon.